In this paper we present an
approach to coordinate the motions of droplets in digital microfluidic systems,
a new class of lab-on-a-chip systems for biochemical analysis. A digital
microfluidic system typically consists of a planar array of cells with electrodes
that control the droplets. The primary challenge in using droplet-based
systems is that they require the simultaneous coordination of a potentially
large number of droplets on the array as the droplets move, mix, and split.
In this paper we describe a general-purpose system that uses simple algorithms
and yet is versatile. First, we present a semi-automated approach to generate
the array layout in terms of components. Next, we discuss simple algorithms
to select destination components for the droplets and a decentralized scheme
for components to route the droplets on the array. These are then combined
into a reconfigurable system that has been simulated in software to perform
analyses such as the DNA polymerase chain reaction. The algorithms have
been able to successfully coordinate hundreds of droplets simultaneously
and perform one or more chemical analyses in parallel. Because it is challenging
to analytically characterize the behavior of such systems, simulation methods
to detect potential system instability are proposed.